laser measurement of distortion |
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odc04r
Old Croc Joined: 12 July 2006 Location: Sarfampton Status: Offline Points: 5483 |
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There are tons of scientific papers out there that describe using laser/accelerometer systems to either measure a drivers distortion or reduce it using a feedback loop. Quite interesting stuff. If you really wanted to have a go then I expect you could get the optics and test gear required for a few £k second hand and put together a little measurement rig. The easiest method by far is a tiny wireless accelerometer with fast data acquisition which I think I mentioned as the best solution the last time this came up. Dirt cheap, lots of data, only one PC needed to process it afterwards and does not need to be real time either. Only downside is a small added mass on the driver. I would definitely start here if I was serious about driver position sensing - or maybe a pressure sensor inside the enclosure.
A complete system with integrated enclosure feedback wouldn't be worth the cost/benefit analysis in the real world where risk of failure is high, cost is high, users don't want the data produced, and the empirical end gig result is all that counts. As mentioned earlier, some highly specialised products (M-Force) are starting to use sensing in their enclosures but it is not going to reach the more amateur end user anytime soon. As Elliot said, simple methods produce good results. Take more drivers than needed, do not run them outside of the region where Bl behaves linearly, much less distortion. |
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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not all distortion comes from the cone - throat distortion, cabinet resonance etc
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Elliot Thompson
Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5172 |
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Lets not forget the source material. Recording/Mastering engineers are flocking to plug-ins that offer some means of sound degradation to make their work sound less Digital and more Analogue.
Spotty Frequency Response from speakers in which many try to rectify with heavy equalisation. It really doesn't make sense trying to achieve 16 kHz from a driver that is -20 dB @ 16 kHz but, many do it anyway. Best Regards, Edited by Elliot Thompson - 05 January 2016 at 7:16pm |
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Elliot Thompson
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fede
Registered User Joined: 07 April 2013 Status: Offline Points: 18 |
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Ipal is awesome because it is for sub bass range only where the cone is like a piston.. This is the first condition.
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70,s hero
Young Croc Joined: 14 December 2014 Location: bristol Status: Offline Points: 637 |
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Yes, I am sure that he could design such a product, I see the laser being attached behind the cone within the enclosure as it only needs a point of reference, it would not interfere with the cone in any way or add mass. Obviously the accelerometer type system adds mass to the cone which sort of defeats the process marginally,the correction signal to any distortion has to be a greater magnitude to take account of the introduced mass.The frequencies are quite low though and so the cone travels at a slower speed in sub. So IMO an ipal system is only suitable for sub as adding an accelerometer to a high/mid frequency driver would be very counter productive. Taking Power softs concept forward, I guess that if they are quite serious about sound and they are, then we may see a laser type control system in the future. I am seeing the laser design fella some time over the next couple of weeks so I will ask him what he thinks about it all. If it all stacks up, then I may be interested in developing such a system and will be happy to get anyone else on board who is interested. |
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Top banana
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mark_in_manc
Registered User Joined: 13 February 2016 Location: Manchester UK Status: Offline Points: 15 |
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I used to work in a lab which had a Polytec scanning laser interferometer. They're very useful for looking at motion of structures where adding an accelerometer would mass-load things to an unacceptable degree - like cone modes (break-up), for example. More on-topic, a cheaper and more simple, non-scanning system for looking at the non-linear volts-velocity relationship in drivers was introduced a few years ago by a German called Klippel - he's a nice guy and has published a large number of academic papers on driver non-linearities, which industry can now measure by buying his analyser :)
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